Energy conservation potential in stainless steel making by use of molten pig iron and liquid ferro-chrome

摘要

Stainless steel is mostly manufactured by Electric Arc Furnace –Argon Oxygen Decarburization route utilising 100% solid charge of steel scrap/DRI/stainless steel scrap and ferroalloys. The process consumes around 415/450 KWH of power per ton of stainless steel. In the state of Odisha, we are endowed with both iron and chromite ores, which offer opportunity for use of molten pig iron and liquid ferrochrome for energy efficient stainless steel making for a plant located there. This paper analyses potential for energy conservation in EAF for three different grades of stainless steel belonging to AISI 200,300,400 series. In this concept, melting is performed in two different furnaces, one EBT type and the other Spout type. In EBT furnace only high ferrous melt with liquid pig iron and DRI/Scrap are charged and dephosphorized. In the spout furnace high carbon ferrochrome which has a tendancy to solidify rapidly due to its high melting point of nearly 1575°C is diluted with scrap which brings down its melting point drastically to enable it to be kept molten. Silicon in the high carbon ferrochrome is gainfully utilised to raise the temperature of molten pool. The diluted ferrochrome is taken in ladle in appropriate portion to which dephosphorised decarburized molten steel is added from EBT furnace for charging into AOD. The material and energy balance have been carried out for the entire charge mix using classical approach of energy calculation. Both variants of DRI and scrap addition to hot metal have been considered for the EBT furnace. Calculations for EBT furnace have been validated using data from an existing carbon steel plant using similar practice of steel making. Calculated values for such energy efficient stainless steel making have been compared with data on existing stainless steel plant using solid charge. Energy usage can be reduced by more than 60% with this approach.